Do thermal treatments influence the ultrafast opto-thermal processes of eumelanin?

Abstract

After light absorption melanin converts very rapidly the energy gained into heat. The time scale of this process ranges from tens of femtoseconds to a few nanoseconds. Femtosecond transient absorption allows for exploration of such photoinduced carrier dynamics in order to observe the de-excitation pathways of the biological complex.

Ultrafast spectral hole burning reveals the distinct chromophores in eumelanin and their common photoresponse

“…2. A more recent TA spectrum reported by Brunetti et al 25 for Sepia melanin in DMSO-methanol (20:1) excited at 350 nm appears to vary smoothly across the visible spectrum in agreement with ours. However, detailed comparison is not possible because the TA signals in ref.…”

“…7a). Whereas the authors of previous TA studies t their kinetic traces to 2 or 3 exponentials, 21,25,41 a log-log plot (Fig. 7b) reveals that the kinetics are actually biphasic in nature, and better ts are obtained with a similar number of parameters using a linear combination of a stretched exponential and a power law,…”

“…However, detailed comparison is not possible because the TA signals in ref. 25 are presented as a two-dimensional timewavelength heat or color map. The maximum in our spectrum at $700 nm is in rough agreement with the maximum of 625 nm reported in ref.…”

“…The maximum in our spectrum at $700 nm is in rough agreement with the maximum of 625 nm reported in ref. 25.…”

“…8,19,20 Thus, top-down studies are crucial for studying how heterogeneity affects the excited state dynamics of eumelanin. To this end, transient absorption 2,[19][20][21][22][23][24][25] and photoluminescence 10,17,26,27 studies of natural and synthetic eumelanins have been carried out, but it has proven difficult to link dynamical observations with structural models.…”